[GRASS-user] new user question about mapsets, locations, and coordinate systems

[Glynn Clements]

mtnbiketrail at zzz.com wrote:

> What I meant was: Is each LOCATION typically a different project?(one 
> LOCATION for ex. for Ohio, and another unrelated LOCATION for Utah. 
> LOCATIONS do not ever cross or mix with each other? And I guess on the 
> URL you gave me on the wiki site, that is a yes.

Each location has projection information and a default region. Mapsets
within a location all share the same projection. This means that you
can use maps from several mapsets in the same command, as they all
share the same coordinate system.

Most commands cannot use maps from more than one location. The main
exceptions are those which are specifically designed to perform
spatial transformations, e.g. r.proj, v.proj, i.rectify, etc, which
read maps from one location and write them to another location,
transforming them between the two coordinate systems.

In terms of organising data into projects, use whatever is convenient. 
If all of the data for a project will be in the same coordinate
system, use a location. If most of your projects use the same
coordinate system, you can use one mapset per project. OTOH, if a
project will use source data in various coordinate systems,
necessitating multiple locations, you might want to use a separate
database for the project.

Most commands can access data from other mapsets in the same location. 
A few can access data from other locations in the same mapset. Very
few will access data from other databases.

-- 
Glynn Clements <glynn at gclements.plus.com>